To form wiring of a semiconductor device, typically, an insulating layer is provided on a substrate. The insulating layer has a concave portion formed therein for providing first and second wiring layers. Then first and second wiring layers are sequentially formed. Each of the first and second wiring layers has a uniform thickness. Then the surfaces of the insulating layer, the first wiring layer, and the second wiring layer are flattened by using a cutting tool.
Wiring of the semiconductor is delaminated by an external force such as an ultrasonic wave from an electronic component and a wire. Therefore, the first wiring layer is often made of Ti, which has high adhesibility with the substrate and the insulating layer. And the second wiring layer is made of Cu or Al, which is a highly conductive metal. However, Ti is a difficult-to-cut material, and its machinability is poor. As a result, the life of a cutting tool becomes short.